Preparation

Make marinade:
In blender, combine olive oil, ginger, tarragon, orange juice, zest, salt, and pepper and purée until smooth. In large bowl, combine marinade and pheasant and toss to coat. Cover and refrigerate overnight or up to 48 hours.

Braise pheasant:
In very large Dutch oven over moderately high heat, heat olive oil until hot but not smoking. Remove pheasant pieces from marinade, scraping off excess, and sprinkle with salt and 1/2 teaspoon pepper. Working in batches, sear pheasant pieces until well browned, about 5 minutes per side. Transfer to paper towel-lined platter to drain.

Using tongs or slotted spoon, transfer pheasant to platter and cover with foil to keep warm. Set pot over high heat and bring pan juices to boil. Boil, uncovered, until sauce is well reduced and thickened, about 25 minutes. Taste and add additional salt and pepper, if necessary.

While juices are reducing, prepare caramelized onions and apples:
Bring medium pot of water to boil. Add pearl onions and boil, uncovered, 1 minute. Drain and run under cold water until cool enough to handle; slip off skins.

In small skillet over moderately high heat, heat oil until hot but not smoking. Add onions, apples, sugar, salt, and pepper and stir to combine. Sear, shaking pan occasionally, until onions and apples are dark golden, about 10 minutes. Stir in apple cider, scraping up any browned bits in pan. Reduce heat to low, cover, and cook until onions are fork tender, about 2 minutes more.

Serve:
Spoon some of sauce over pheasant and garnish with onions, apples, and chopped tarragon. Serve additional sauce alongside.